The Dipper Cinclus cinclus and stream acidity: population change, breeding success, and diet in south-western Sweden

Abstract

Breeding Dippers were surveyed at 45 streams in southwestern Sweden in 1974—1978 and in 1990—1992. Dippers bred at 37 streams (65 sites) in 1974—1978 and 38 streams (74 sites) in 1990—1992. The breeding frequency, and the change in breeding frequency from 1974—1978 to 1990—1992, did not differ between streams with different history of acidity. Also, clutch size and brood size were similar along neutral, formerly acidic, and acidic streams. We analysed by faeces the diet of adult Dippers in 30 breeding pairs in 1991. Their diet at neutral, formerly acidic and acidic streams showed no clear differences; preferred prey seemed to be available even on acidic streams. So, in contrast to studies in Scotland and Wales, we found no apparent effects of stream acidity on breeding Dippers in this pilot study.